The film market demands polypropylene resins that can produce a special combination of film properties. For applications involving thermal cycles, films with good heat resistance and good mechanical properties are required. The features of polyethylene and polypropylene semi-crystalline polymers are such that they cover a wide range of properties and potential applications. The density of polyethylene is from 0.92 g/cc to 0.97 g/cc with a melting temperature between 110° C. for low density polyethylene to 135° C. for high density polyethylene. On the other hand, the density of isotactic polypropylene is 0.89 to 0.91 g/cc with a melting temperature of 163° C. The physical properties of isotactic polypropylene can be determined by its degree of tacticity (or crystallinity) and by its molecular weight distribution. Because of the relatively high melting temperature of the crystalline phase, polypropylene retains its mechanical strength up to rather high temperatures.
Achieving a heat resistant propylene polymer film for applications involving thermal cycles is desirable. Producing a heat resistant film that has the necessary tear, impact, and puncture resistance is also desirable.